The invention concerns a fine-focusing stage for microscopes, with an object carrier, a holder for the object carrier, and a positioning means which changes the vertical Z-axis position of the object carrier.
In ordinary microscopy, the object is focused by the microscope focusing drive. Positioning accuracy attainable with motors--usually DC motors--is about .+-.50 nm. Such values are inadequate, by a factor of more than two, so such focusing is not useful. External stepping motors are also often attached to the fine focusing drive of the microscope. By gearing down sufficiently, fine step divisions can be achieved; but the internal or external gearing needed very substantially limits movability.
Gear-free direct drives are already known in practice. Positioning accuracies in the nanometer range are attained with such direct drives. However, the range of motion is limited to a few hundred micrometers. There is the further problem here that such a direct drive, for instance, moves only one objective, which then projects far past the other objectives.
Z-stages which can be moved by piezoactive elements are also known in practice. However, the range of movement of such Z-stages is limited by the piezoelements. Piezo assemblies are also expensive because of the external measurement system required and because of the high-voltage control systems also needed.
Almost any desired Z scan rates can be attained with piezo control, including constant rapid and also very slot Z scan rates, such as 1000 .mu.m per second to 0.01 .mu.m per second. Speed tolerances less than .+-.0.5% can, in any case, be attained with geared motors only with extreme difficulty.
Now if a fine-adjustment stage is to be used in a conventional microscope, its design requires extreme flatness, with heights of about 5 mm desirable. Also, there must be a hole in the center of the stage for the light to pass through.
Z-stages with galvanometrically driven tilt plates have also been known in practice for some years. The disadvantage of such a system, though, is that the object is necessarily moved laterally as it is lifted, with large lift movements. If the object being observed is in the plane of the pivot of the tilt plate the error due to the lateral movement is negligibly small. For objects, or areas of objects, more distant from the plane of pivoting, though, this error becomes unacceptably large as the distance increases.